1. Field of the Invention
The present invention relates to the design and fabrication of a fan-out unit which connects a thin-film transistor (TFT) array on a substrate with input/output IC circuitry for an LCD display system.
2. Description of the Related Art
Liquid crystal displays (LCDs) are among the most widely used flat panel displays. An LCD consists of a common electrode substrate, a control substrate having a thin-film transistor (TFT) array pattern, and a layer of liquid crystal solution sandwiched in between the substrates. When a voltage related to image data is applied across the liquid crystal layer in each pixel, an incident light is allowed to pass through in varying amounts according to the image data, thus constituting different levels of display intensity in the pixel. Therefore, a sequence of voltages corresponding to an image data array can generate a desired image on an LCD screen.
A fan-out unit is used to connect a group of gate lines or a group of data lines to a gate integrated circuit (IC) or a data IC and is typically formed in a peripheral region of a TFT array substrate. Usually the channels in a fan-out unit have different lengths and thus can have non-uniform resistance values among the gate lines or data lines, which affects image consistency. Therefore, it is desired to equalize the fan-out channel lengths.
In the past, the fan-out channels were arranged in zigzag forms to equalize the channel resistance. However, size and density of LCD have been increasing, and the channel numbers continue to grow on the ever shrinking edge spaces available for the fan-out circuitry. Consequently, there is little room left to improve resistance variation by adjusting the channel lengths only. Furthermore, a zigzag wire form bends a channel and increases its resistance. Thus, it is desired to minimize the channel bending.